The present invention relates generally to iron-type golf clubs and, more particularly, to golf club heads configured to impart improved feel to the golfer and improved transfer of energy to a golf ball.
After the initial drive from a tee, a golfer usually relies upon his or her set of irons to reach the green, where one or more putts typically finish the hole. A set of irons typically includes irons having loft angles ranging from about 17xc2x0 for low numbered or long irons, through about 50xc2x0 for higher numbered or short irons, and typically also includes at least a pitching wedge. The increasing loft angles generally cause the golf ball to have a higher launch angle and a higher spin rate. These irons are used primarily for distance down the fairway, as contrasted for example with lob or sand wedges, and therefore are typically designed differently from the higher lofted wedges, which typically have loft angles in the range of about 52 to 60xc2x0.
Traditional iron-type golf club heads typically have blade-like shapes, often of a forged steel. This style of head typically includes an upper part that is blade-like and a lower part that is uniformly triangular in cross-section at the rear of the head. The resulting lower mass concentration combines with the loft angle to aid the golfer in getting the club head under the golf ball, particularly in sand or tall grass areas. However, the overall mass distribution can result in a hard feeling upon contact with a golf ball, which is unpleasant to many golfers. Generally, golfers prefer irons having a relatively xe2x80x9csoftxe2x80x9d feel. They also prefer irons that provide feel feedback on the appropriate swing and contact with the ball, in order to achieve the desired ball travel distance.
Another prior iron-type golf club head design removes some mass from the rear of the head, at both the toe area and the heel area, to create two pockets or recesses. This forms a center peak at the rear of the club head. In one such design, the toe and heel end masses and the center peak extend to an upper position, toward the topline, at the rear of the club head. The increase in thickness of the center peak relative to the upper part of the club head is limited in order not to substantially increase the head""s weight. Another prior iron-type golf club design has minimal amounts of mass removed from the toe and/or heel areas, so as to form a cosmetic feature that does not differ substantially from the previous, conventional design. In both recess designs, the higher positioned mass at the rear tends to stiffen the club head.
A currently popular style is a perimeter-weighted, cavity-back iron, which often is made of a cast steel alloy. The perimeter weighting results in a more forgiving structure for mis-hits, and it is preferred by many golfers. Again, however, the perimeter mass can cause sufficient rigidity to result in undesired vibration being felt by the golfer. Such undesired vibrations also can occur even in head designs having a thickened portion at the rear of the head, behind the impact area.
Thus, one undesirable characteristic that is common both to forged, blade-like iron heads and to cast, cavity-back iron heads is a harsh vibration of the head. This vibration also is indicative of uncontrolled energy transfer upon impact with the golf ball. It should, therefore, be appreciated that there is a need for an improved golf club iron head that reduces such undesired vibrations. The present invention fulfills this need.
The present invention provides an iron-type golf club head providing enhanced flexibility and selectively increased stiffness, for improved performance and feel. That is, the relative stiffness in the lower portion of the club head, varying from heel to toe, is designed in conjunction with a reduced top stiffness that results in improved vibration characteristics. The vibration is an indication of the energy transmission through the club head upon impact with a golf ball. Thus, the present invention optimizes the channeling of the energy that is felt as vibration, or heard as sound, by the golfer by configuring the club head to have discrete stiffened portions. This effect of these discrete stiffened portions has been found to be of greater significance than is the effect of forming the club head of a forged material or a cast material.
A preferred embodiment of a golf club head of the present invention comprises a body having an upper portion and a rearwardly extending lower portion. The upper portion has a top edge, and the lower portion has a bottom edge. The striking face has a length, and a rear side of the lower portion has at least a first recess adjacent a toe end and at least a second recess adjacent a heel end of the head. The loft angle of the club head is between about 17xc2x0 and 50xc2x0.
Preferably, the upper portion of the body tapers such that a first stiffness at its upper end provides a maximum stiffness for the upper portion. A second stiffness at its lower end provides a minimum stiffness for the upper portion.
A lateral axis is defined at the junction between the upper and lower portions of the body, extending from the toe end to the heel end. A reference point is defined at a mid portion of the lateral axis, between about 55% and about 75% of the height of the striking face, as measured from the bottom edge to the top edge. A central axis is defined substantially parallel to the lateral axis, at approximately 50% of the face height.
The first recess comprises a first volume and the second recess comprises a second volume, and the first and second recesses extend at least to the central axis. The portions of the body that define the first and second recesses preferably each have a stiffness no more than 90% greater than a minimum stiffness of the upper portion. The remainder of the lower portion preferably has a stiffness at least 230% greater than the stiffness of at least one of the first and second recesses.
In the preferred embodiment, the central region of the lower portion, located below the reference point, has a maximum stiffness that is at least about 30 times a maximum stiffness of the upper portion. The regions below the first and second recesses each have a maximum stiffness at least about 20 times the maximum stiffness of the upper portion. A stiffness zone is defined within the central region, at the central axis, and it extends halfway toward the lateral axis, between the first and second recesses. The zone extends at least about 20% of the length of the striking face, such that a relative stiffness is established between the central region and the upper portion and between the central region and the first and second recesses.
Other features and advantages of the present invention should become apparent from the following description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.